Osmotic therapeutic dispensers for the precision administration of drugs with control of their delivery patterns and with extended delivery times are known in U.S. Pat. No. 3,845,770 issued to patentee Theeuwes and Higuchi, and in U.S. Pat. No. 3,916,899 issued to the same patentee. The dispensers disclosed in these patents are made of a semipermeable wall that surrounds a compartment containing a drug. The semipermeable wall is permeable to the passage of an external fluid, impermeable to the passage of drug, and it has a portal for dispensing drug from the dispenser.
In U.S. Pat. Nos. 4,036,227; 4,093,708; 4,096,238; 4,135,54; and 4,142,526, all issued to patentee Zaffaroni, Michaels, and Theeuwes, an improvement is disclosed in the osmotic dispensers of U.S. Pat. Nos. 3,845,770 and 3,916,899. The improvement comprises an enteric layer, which does not disintegrate in the stomach but disintegrates in the intestine, coated onto the exterior surface of the semipermeable wall of the dispenser. The dispenser coated entirely with the enteric layer releases drug only in the intestine, and not in the stomach.
The above dispensers represent an outstanding and a pioneer advancement in the osmotic dispensing art, and they are useful for dispensing innumerable drugs to the environment of use. Now, it has been found the dispenser can be unexpectedly improved leading to more desirable results. For example, it will be appreciated by those versed in the dispensing art that if a novel and useful dispenser is made available for delivering drug at a rate or rates precisely controlled by the dispenser which rate or rates are in response to the biological environment within which it functions, such a dispenser would have a positive clinical value, and also represent a substantial contribution in the dispensing art.